1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having the properties of reduced power consumption by being driven with a low driving voltage, and a fast response time.
2. Discussion of the Related Art
Generally, since LCD devices are driven with a low operating voltage, LCD devices have low power consumption and are used as portable devices. Accordingly, LCD devices are widely applied to various fields such as notebook computers, monitors, spacecrafts, airplanes, etc.
LCD devices include a lower substrate, an upper substrate, and a liquid crystal layer formed therebetween. In LCD devices, the alignment of liquid crystal in a liquid crystal layer is adjusted with an electric field, and thus, light transmittance of the LCD device is adjusted, thereby displaying an image.
LCD devices are variously developed in a twisted nematic (TN) mode, a vertical alignment (VA) mode, an in-plane switching (IPS) mode, or a fringe field switching (FFS) mode depending on a scheme of adjusting the alignment of liquid crystal.
Among the modes, the IPS mode and the FFS mode are modes in which a plurality of pixel electrodes and common electrodes are arranged on a lower substrate, and thus, the alignment of liquid crystal is adjusted with electric fields between the pixel electrodes and the common electrodes.
The IPS mode is a mode in which a plurality of pixel electrodes and common electrodes are alternately arranged in parallel, and thus, lateral electric fields are respectively generated between the pixel electrodes and the common electrodes, thereby adjusting the alignment of liquid crystal. The FFS mode is a mode in which a pixel electrode and a common electrode is formed to be separated from each other with an insulating layer therebetween, one of the pixel electrode and common electrode is formed in a plate shape, and the other is formed in a finger shape, thereby adjusting the alignment of liquid crystal with fringe fields generated between the pixel electrodes and the common electrodes.
Hereinafter, a related art IPS-mode LCD device will be described with reference to FIG. 1.
FIG. 1 is a sectional view schematically illustrating the related art IPS-mode LCD device.
As seen in FIG. 1, the related art IPS-mode LCD device includes an upper substrate 10, a lower substrate 20, a sealant 30, and a liquid crystal layer 40.
A light blocking layer 12, a color filter layer 14, and an overcoat layer 16 are sequentially formed on the upper substrate 10.
The light blocking layer 12 prevents leakage of light to an area other than a pixel area, and is formed in a matrix structure.
The color filter layer 14 is formed on the light blocking layer 12, and includes a plurality of red (R), green (G), blue (B) color filters.
The overcoat layer 16 is formed on the color filter layer 14, and planarizes a substrate.
An array layer 22, a plurality of pixel electrodes 24, and a plurality of common electrodes 26 are formed on the lower substrate 20.
The array layer 22 includes a plurality of gate lines (not shown) and a plurality of data lines (not shown) which intersect each other to define a plurality of pixel areas, and a plurality of thin film transistors (TFTs) that are respectively formed in the pixel areas defined by intersections of the gate lines and data lines.
The pixel electrodes 24 are formed on the array layer 22, and are electrically connected to the respective TFTs inside the array layer 22.
The common electrodes 26 are formed on the array layer 22, and generate electric fields together with the pixel electrodes 24 to drive the liquid crystal layer 30.
The sealant 30 is formed between the upper substrate 10 and the lower substrate 20. The upper substrate 10 is adhered to the lower substrate 20 by the sealant 30.
The liquid crystal layer 40 is formed between the upper substrate 10 and the lower substrate 20. In the liquid crystal layer 40, alignment of liquid crystal is adjusted according to a direction of an electric field generated by the pixel electrode 24 and the common electrode 26.
However, the related art IPS-mode LCD device has the following limitations. Generally, it may be desired to drop a driving voltage of an LCD device to reduce the power consumption of the LCD device. The liquid crystal for the liquid crystal layer 40 may be used to drop the driving voltage of the LCD device when the absolute value of dielectric anisotropy (Δ∈=∈//−∈⊥) of the liquid crystal is high. As an example, when positive liquid crystal is used as the liquid crystal of the liquid crystal layer 40, the driving voltage may be further dropped in cases, where dielectric anisotropy (Δ∈) is 4, compared with cases where dielectric anisotropy (Δ∈) is 3. As another example, when negative liquid crystal is used as the liquid crystal of the liquid crystal layer 40, the driving voltage may be further dropped in cases where dielectric anisotropy (Δ∈) is −4, compared with cases where dielectric anisotropy (Δ∈) is −3.
However, when the negative liquid crystal having a high absolute value of dielectric anisotropy (Δ∈=∈//−∈⊥) is used for dropping a driving voltage, the rotational viscosity of the liquid crystal may substantially increase and thus, the response time of the liquid crystal may become slower.